Effects of perceptual and working memory load on brain responses to task-irrelevant stimuli: Review and implications for future research

Investigating the effects of focused attention (mantra) meditation on mismatch negativity: Insights into sensory and cognitive processing using an intensity oddball paradigm

Over the past fifty years, research has enhanced our understanding of meditation and its effects on cognition. Meditation is particularly promising due to its long-term (trait) effects, which persist outside meditation sessions. Advances in neuroimaging have enabled the study of these effects using neural markers such as mismatch negativity (MMN), which reflects the involuntary shift of attention to unexpected acoustic changes. This shift is modulated by attentional control, a key area where focused attention (FA) meditation training offers improvements. However, studies investigating the trait effects of FA meditation on MMN have produced mixed results, with previous research introducing confounds from short-term (state) effects that may influence trait-specific assessments. Furthermore, most research has focused on breath-based FA meditation, overlooking other prominent forms of FA meditation that might differentially modulate MMN, as per recent studies. The current study, therefore, examines mantra meditation, a widely practiced form of FA meditation, with an adequately powered sample to address the mixed findings in the literature. The study employs an intensity oddball paradigm instead of commonly used frequency oddball paradigms to assess whether MMN arises from higher-order cognitive processes or sensory adaptation. The findings reveal similar MMN amplitude in experts and novices, suggesting that MMN may be insensitive to meditation expertise or influenced by the enhanced attentional skills of novices. Additionally, a unidirectional polarity shift in event-related potential to deviant stimuli suggests that meditation effects on MMN should be interpreted in the context of higher-order deviance detection mechanism.

Causal evidence for increased theta and gamma phase consistency in a parieto-frontal network during the maintenance of visual attention

Endogenous visuo-spatial attention is under the control of a fronto-parietal network of brain regions. One key node in this network, the intra-parietal sulcus (IPS), plays a crucial role in maintaining endogenous attention, but little is known about its ongoing physiology and network dynamics during different attentional states. Here, we investigated the reactivity of the left IPS in response to brain stimulation under different states of selective attention. We recorded electroencephalography (EEG) in response to single pulses of transcranial magnetic stimulation (TMS) of the IPS, while participants (N = 44) viewed bilateral random-dot motion displays. Individual MRI-guided TMS pulses targeted the left IPS, while the left primary somatosensory cortex (S1) served as an active control site. In separate blocks of trials, participants were cued to attend covertly to the motion display in one hemifield (left or right) and to report brief coherent motion targets. The perceptual load of the task was manipulated by varying the degree of motion coherence of the targets. Excitability, variability and information content of the neural responses to TMS were assessed by analysing TMS-evoked potential (TEP) amplitude and inter-trial phase clustering (ITPC), and by performing multivariate decoding of attentional state. Results revealed that a left posterior region displayed reduced variability in the phase of theta and gamma oscillations following TMS of the IPS, but not of S1, when attention was directed contralaterally, rather than ipsilaterally to the stimulation site. A right frontal cluster also displayed reduced theta variability and increased amplitude of TEPs when attention was directed contralaterally rather than ipsilaterally, after TMS of the IPS but not S1. Reliable decoding of attentional state was achieved after TMS pulses of both S1 and IPS. Taken together, our findings suggest that endogenous control of visuo-spatial attention leads to changes in the intrinsic oscillatory properties of the IPS and its associated fronto-parietal network.

The effect of text and graphic cue-based action observation on the working memory performance of novice badminton players

Introduction

Understanding strategic situations is essential in sports. There has been relatively little research examining the effectiveness of action observation based on visual cues in strategic situations. This study investigated whether action observation with visual cues can help performers understand the strategic aspects of complex sports by analyzing the effect of text cue-based action observation and graphic cue-based action observation on the accuracy and speed of cognitive information processing in working memory.

Methods

Forty-four male and female novice badminton players participated in the experiment. They were randomly assigned to one of four groups: text cue-based action observation (TAO), graphic cue-based action observation (GAO), action observation (AO), and a control group (CON). The experimental design consisted of a pre-test, intervention, and post-test. The experiment analyzed the accuracy and response time of cognitive information processing in working memory.

Results

The accuracy and response time analysis showed that the AO group significantly improved their cognitive performance accuracy and response time from pre-test to post-test compared to the control group. The TAO and GAO groups with visual cues significantly outperformed the AO and CON groups for accuracy. However, only the TAO group significantly outperformed the other groups in term of response time. The GAO group improved significantly compared to the CON group but not significantly compared to the AO.

Conclusion

These results suggest that visual cues can influence the modulation of cognitive load in working memory and that TAO is a relatively more efficient perceptual-cognitive training method for novices.

Attenuated processing of task-irrelevant speech and other auditory stimuli: fMRI evidence from arithmetic tasks

When performing cognitive tasks in noisy conditions, the brain needs to maintain task performance while additionally controlling the processing of task-irrelevant and potentially distracting auditory stimuli. Previous research indicates that a fundamental mechanism by which this control is achieved is the attenuation of task-irrelevant processing, especially in conditions with high task demands. However, it remains unclear whether the processing of complex naturalistic sounds can be modulated as easily as that of simpler ones. To address this issue, the present fMRI study examined whether activity related to task-irrelevant meaningful speech is attenuated similarly as that related to meaningless control sounds (nonsense speech and noise-vocoded, unintelligible sounds). The sounds were presented concurrently with three numerical tasks varying in difficulty: an easy control task requiring no calculation, a 'routine' arithmetic calculation task and a more demanding 'creative' arithmetic task, where solutions are generated to reach a given answer. Consistent with their differing difficulty, the tasks activated fronto-parieto-temporal regions parametrically (creative > routine > control). In bilateral auditory regions, activity related to the speech stimuli decreased as task demands increased. Importantly, however, the attenuation was more pronounced for meaningful than nonsense speech, demonstrating that distractor type can strongly modulate the extent of the attenuation. This also suggests that semantic processing may be especially susceptible to attenuation under conditions with increased task demands. Finally, as this is the first study to utilize the 'creative' arithmetic task, we conducted exploratory analyses to examine its potential in assessing neural processes involved in mathematical problem-solving beyond routine arithmetic.

The immediate and lasting effects of imagery rescripting and their associations with imagery tendency in young adults with childhood maltreatment history: An ERP study

The effectiveness of imagery rescripting (IR) in reducing psychological symptoms associated with aversive memories has been confirmed across various disorders. To better understand the neural mechanisms underlying IR, we assessed the immediate and lasting effects and their associations with imagery tendency by using unpleasant pictures depicting child maltreatment within a population with childhood maltreatment (CM) history. Participants (n = 68) were instructed to engage in two experimental phases while electroencephalogram was recorded. In the rescripting phase, participants viewed neutral or unpleasant pictures and then either imagined the same pictures or rescripted unpleasant ones to assess immediate effect. In the re-exposure phase, participants passively viewed all pictures without instruction to assess lasting effect. Participants rated their subjective valence and imagery vividness in the rescripting phase or intensity of negative feelings in the re-exposure phase. IR led to an attenuation of the late positive potential (LPP) amplitude in the late time window (2000-6000 ms at parietal-occipital electrodes) and a decrease in self-reported unpleasantness during the rescripting phase. After 5-min interval, unpleasant pictures with rescripted history elicited smaller LPP (400-1500 ms at centro-parietal electrodes) and negative feelings than those with imagery history in the re-exposure phase. The higher habitual use of imagery was associated with a greater reduction in late LPP during the rescripting phase and full-time range LPP during the re-exposure phase. The current findings suggest that IR has an immediate effect and a lasting effect on subjective and neural response in the CM population. Individuals with higher imagery tendency are likely to profit more from IR.

The impact of stimulus format and presentation order on social working memory updating

Emotional faces and words have been extensively employed to examine cognitive emotional processing including social working memory, which plays a pivotal role in social interactions. However, it remains unclear which exact role these two stimulus formats play in updating specific emotional content, such as positive or negative information. Therefore, the current study examined the differences in working memory updating (WMU) of negative, neutral, and positive faces (Experiment 1) and words (Experiment 2), using a classic two-back paradigm with an event-related potential technique. In both experiments, emotional stimuli were presented in the same or different-valence order to further determine whether presentation order can also influence the WMU of specific emotional content. Our results showed that both stimulus format and presentation order play a role: (a) while faces showed an affective bias [larger P2 and late positive potential (LPP) for negative and positive faces than for neutral faces], words showed a negativity bias (larger LPP for negative words than both neutral and positive words); (b) While faces showed better performance with same-valence order, words showed better performance with different-valence order. Taken together, our findings indicate that, even if faces and words can contain the same emotional information, they impact social WMU differently.

Using mobile EEG to study auditory work strain during simulated surgical procedures

Surgical personnel face various stressors in the workplace, including environmental sounds. Mobile electroencephalography (EEG) offers a promising approach for objectively measuring how individuals perceive sounds. Because surgical performance does not necessarily decrease with higher levels of distraction, EEG could help guide noise reduction strategies that are independent of performance measures. In this study, we utilized mobile EEG to explore how a realistic soundscape is perceived during simulated laparoscopic surgery. To examine the varying demands placed on personnel in different situations, we manipulated the cognitive demand during the surgical task, using a memory task. To assess responses to the soundscape, we calculated event-related potentials for distinct sound events and temporal response functions for the ongoing soundscape. Although participants reported varying degrees of demand under different conditions, no significant effects were observed on surgical task performance or EEG parameters. However, changes in surgical task performance and EEG parameters over time were noted, while subjective results remained consistent over time. These findings highlight the importance of using multiple measures to fully understand the complex relationship between sound processing and cognitive demand. Furthermore, in the context of combined EEG and audio recordings in real-life scenarios, a sparse representation of the soundscape has the advantage that it can be recorded in a data-protected way compared to more detailed representations. However, it is unclear whether information get lost with sparse representations. Our results indicate that sparse and detailed representations are equally effective in eliciting neural responses. Overall, this study marks a significant step towards objectively investigating sound processing in applied settings.

The neuronal signature of surprised facial expression processing under different attentional focuses: A time-domain and time-frequency study

Previous studies have shown that high-arousal positive and negative facial expressions influence event-related potential (ERP) and time-frequency responses depending on attentional focuses. However, little is known about how relevant neural responses are influenced by surprised facial expressions, which are also high in arousal but ambiguous in valence. To address the issue, 38 participants were presented with surprised, happy, angry and neutral facial expressions. Attention was manipulated to focus on facial emotional attributes, facial non-emotional attributes, non-facial attributes, or was free to the participants. ERP results showed larger N170 responses to surprised compared to neutral facial expressions when attention focused on facial attributes and to surprised compared to angry and neutral facial expressions when attention focused on facial non-emotional attributes. Time-frequency analyses revealed reduced power of early occipital theta to surprised compared to happy and angry expressions when attention focused on facial emotions and to surprised compared to angry expressions when attention focused on non-facial stimuli. Parietal delta power was smaller for surprised facial expressions than for angry facial expressions when attention focused on facial emotions and for surprised facial expressions than for angry and neutral facial expressions when attention was directed to non-facial stimuli. These findings might suggest that neural responses to surprised facial expressions are modulated by attentional focus.

Emotional interference and attentional control in schizophrenia-spectrum disorders: The special case of neutral faces

BACKGROUND AND OBJECTIVES

Schizophrenia-spectrum disorders (SSD) are characterized by impaired emotion processing and attention. SSD patients are more sensitive to the presence of emotional distractors. But despite growing interest on the emotion-attention interplay, emotional interference in SSD is far from fully understood. Moreover, research to date has not established the link between emotional interference and attentional control in SSD. This study thus aimed to investigate the effects of facial expression and attentional control in SSD, by manipulating perceptual load.

METHODS

Twenty-two SSD patients and 22 healthy controls performed a target-letter discrimination task with task-irrelevant angry, happy, and neutral faces. Target-letter was presented among homogenous (low load) or heterogenous (high load) distractor-letters. Accuracy and RT were analysed using (generalized) linear mixed-effect models.

RESULTS

Accuracy was significantly lower in SSD patients than controls, regardless of perceptual load and facial expression. Concerning RT, SSD patients were significantly slower than controls in the presence of neutral faces, but only at high load. No group differences were observed for angry and happy faces.

LIMITATIONS

Heterogeneity of SSD, small sample size, lack of clinical control group, medication.

CONCLUSIONS

One possible explanation is that neutral faces captured exogenous attention to a greater extent in SSD, thus challenging attentional control in perceptually demanding conditions. This may reflect abnormal processing of neutral faces in SSD. If replicated, these findings will help to understand the interplay between exogenous attention, attentional control, and emotion processing in SSD, which may unravel the mechanism underlying socioemotional dysfunction in SSD.

Positive emotion up-regulation is resistant to working memory load: An electrocortical investigation of reappraisal and savoring

Studies of emotion regulation to-date have mostly focused on negative emotion down-regulation, leaving positive emotion up-regulation poorly understood, particularly regarding factors that may modulate its success. While reappraisal and savoring have been shown to be effective at increasing electrocortical and subjective response to pictures in controlled laboratory settings, it remains unclear whether individuals can effectively enact these techniques to willfully increase positive emotions in everyday life when faced with other concurrent distractions/demands. Here, we used the late positive potential (LPP), an electrocortical measure that is larger for emotional compared to neutral stimuli, to assess the effect of working memory (WM) load on individuals' ability to reappraise or savor positive pictures. Seventy-six participants were randomly assigned to use either reappraisal or savoring to up-regulate positive emotion to pictures. Following training, participants engaged in a positive emotion up-regulation task interspersed with high and low WM load trials, while EEG was recorded. Frequentist and Bayesian statistics showed that although high WM load seemed to consume resources and reduced picture processing overall, it did not interfere with the enhancement of the LPP via positive emotion up-regulation. Nonetheless, WM performance (especially on high-load trials) was worse when participants were engaged in positive emotion up-regulation. Therefore, while both techniques appear to be effective under concurrent WM load, positive emotion up-regulation may interfere with other ongoing tasks.

The effect of working memory load on inattentional deafness during aeronautical decision-making

Operating an aircraft requires pilots to handle a significant amount of multi-modal information, which creates a high working memory load. Detecting auditory alarms in this high-load scenario is crucial for aviation safety. According to cognitive control load theory, an increase in working memory load may enhance distractor interference, resulting in improved detection sensitivity for task-irrelevant stimuli. Therefore, understanding the effect of working memory load on auditory alarm detection is of particular interest in aviation safety research. The studies were designed to investigate the effect of storage load and executive function load of working memory on auditory alarm detection during aeronautical decision-making through three experiments. In Experiment 1 and 2, participants performed an aeronautical decision-making task while also detecting an auditory alarm during the retention interval of a working memory task (visual-spatial, visual-verbal and auditory-verbal). In Experiment 3, participants were required to detect an auditory alarm while performing the 2-back and 3-back aeronautical decision-making tasks. Experiment 1 found that the auditory alarm sensitivity was higher in conditions of low visual-spatial working memory storage load compare to high load conditions. Experiment 2 found that a high storage load of visual-verbal working memory reduced auditory alarm sensitivity but auditory-verbal working memory load did not. Experiment 3 found that, unlike storage load, auditory alarm sensitivity was stronger under high executive function load relative to low executive function load. These findings show that working memory storage load and executive function load have different effects on auditory alarm sensitivity. The relationship between executive function and auditory alarm sensitivity supports cognitive control load theory, while the impact of the storage function on auditory alarm sensitivity does not adhere to this theory.

Target of selective auditory attention can be robustly followed with MEG

Selective auditory attention enables filtering of relevant acoustic information from irrelevant. Specific auditory responses, measurable by magneto- and electroencephalography (MEG/EEG), are known to be modulated by attention to the evoking stimuli. However, such attention effects have typically been studied in unnatural conditions (e.g. during dichotic listening of pure tones) and have been demonstrated mostly in averaged auditory evoked responses. To test how reliably we can detect the attention target from unaveraged brain responses, we recorded MEG data from 15 healthy subjects that were presented with two human speakers uttering continuously the words "Yes" and "No" in an interleaved manner. The subjects were asked to attend to one speaker. To investigate which temporal and spatial aspects of the responses carry the most information about the target of auditory attention, we performed spatially and temporally resolved classification of the unaveraged MEG responses using a support vector machine. Sensor-level decoding of the responses to attended vs. unattended words resulted in a mean accuracy of [Formula: see text] (N = 14) for both stimulus words. The discriminating information was mostly available 200-400 ms after the stimulus onset. Spatially-resolved source-level decoding indicated that the most informative sources were in the auditory cortices, in both the left and right hemisphere. Our result corroborates attention modulation of auditory evoked responses and shows that such modulations are detectable in unaveraged MEG responses at high accuracy, which could be exploited e.g. in an intuitive brain-computer interface.

Visual perceptual load and processing of somatosensory stimuli in primary and secondary somatosensory cortices

Load theory assumes that neural activation to distractors in early sensory cortices is modulated by the perceptual load of a main task, regardless of whether task and distractor share the same sensory modality or not. While several studies have investigated the question of load effects on distractor processing in early sensory areas, there is no functional magnetic resonance imaging (fMRI) study regarding load effects on somatosensory stimuli. Here, we used fMRI to investigate effects of visual perceptual load on neural responses to somatosensory stimuli applied to the wrist in a study with 44 participants. Perceptual load was manipulated by an established sustained visual detection task, which avoided simultaneous target and distractor presentations. Load was operationalized by detection difficulty of subtle or clear color changes of one of 12 rotating dots. While all somatosensory stimuli led to activation in somatosensory areas SI and SII, we found no statistically significant difference in brain activation to these stimuli under high compared to low sustained visual load. Moreover, exploratory Bayesian analyses supported the absence of differences. Thus, our findings suggest a resistance of somatosensory processing to at least some forms of visual perceptual load, possibly due to behavioural relevance of discrete somatosensory stimuli and separable attentional resources for the somatosensory and visual modality.

Cognitive Avoidance Is Associated with Decreased Brain Responsiveness to Threat Distractors under High Perceptual Load

Cognitive coping strategies to deal with anxiety-provoking events have an impact on mental and physical health. Dispositional vigilance is characterized by an increased analysis of the threatening environment, whereas cognitive avoidance comprises strategies to inhibit threat processing. To date, functional neuroimaging studies on the neural underpinnings of these coping styles are scarce and have revealed discrepant findings. In the present study, we examined automatic brain responsiveness as a function of coping styles using functional magnetic resonance imaging. We administered a perceptual load paradigm with contemptuous and fearful faces as distractor stimuli in a sample of N = 43 healthy participants. The Mainz Coping Inventory was used to assess cognitive avoidance and vigilance. An association of cognitive avoidance with reduced contempt and fear processing under high perceptual load was observed in a widespread network including the amygdala, thalamus, cingulate gyrus, insula, and frontal, parietal, temporal, and occipital areas. Our findings indicate that the dispositional tendency to divert one's attention away from distressing stimuli is a valuable predictor of diminished automatic neural responses to threat in several cortical and subcortical areas. A reduced processing in brain regions involved in emotion perception and attention might indicate a potential threat resilience associated with cognitive avoidance.

The effects of visual perceptual load on detection performance and event-related potentials to auditory stimuli

Load Theory states that perceptual load prevents, or at least reduces, the processing of task-unrelated stimuli. This study systematically examined the detection and neural processing of auditory stimuli unrelated to a visual foreground task. The visual task was designed to create continuous perceptual load, alternated between low and high load, and contained performance feedback to motivate participants to focus on the visual task instead of the auditory stimuli presented in the background. The auditory stimuli varied in intensity, and participants signaled their subjective perception of these stimuli without receiving feedback. Depending on stimulus intensity, we observed load effects on detection performance and P3 amplitudes of the event-related potential (ERP). N1 amplitudes were unaffected by perceptual load, as tested by Bayesian statistics. Findings suggest that visual perceptual load affects the processing of auditory stimuli in a late time window, which is associated with a lower probability of reported awareness of these stimuli.

The effects of visual working memory load on detection and neural processing of task-unrelated auditory stimuli

While perceptual load has been proposed to reduce the processing of task-unrelated stimuli, theoretical arguments and empirical findings for other forms of task load are inconclusive. Here, we systematically investigated the detection and neural processing of auditory stimuli varying in stimulus intensity during a stimuli-unrelated visual working memory task alternating between low and high load. We found, depending on stimulus strength, decreased stimulus detection and reduced P3, but unaffected N1 amplitudes of the event-related potential to auditory stimuli under high as compared to low load. In contrast, load independent awareness effects were observed during both early (N1) and late (P3) time windows. Findings suggest a late neural effect of visual working memory load on auditory stimuli leading to lower probability of reported awareness of these stimuli.

Evidence of target enhancement and distractor suppression in early visual areas

Although the mechanisms of target enhancement and distractor suppression have been investigated along the visual processing hierarchy, there remains some unknown as to the role of perceptual load on the competition between different task-related information as attention deployment is manipulated. We present an fMRI spatial cueing paradigm, in which 32 participants had to attend to either a left or a right hemifield location and to indicate the orientation of the target Gabor that was presented simultaneously to a noise patch distractor. Critically, the target could appear at either the cued, valid location or at the uncued, invalid location; in the latter, the noise patch distractor appeared at the cued location. Perceptual load was manipulated by the presence or absence of high-contrast Gabor patches close to the fixation cross, which acted as lateral masks. Behavioural results indicated that participants performed more efficiently in validly cued trials compared to invalidly cued trials and under low compared to high load. Enhancement effects for targets and suppression effects for noise patches were greater in early visual areas at high load, that is in the presence of lateral masks. These results are in line with the hypothesis that attention results in both target enhancement and distractor suppression, and that these effects are most marked under high perceptual load. Theoretical implications of these results for different models of attention are discussed.

Event-related potential patterns of selective attention modulated by perceptual load

INTRODUCTION

A high perceptual load can effectively prevent attention from being drawn to irrelevant stimuli; however, the neural pattern underlying this process remains unclear.

METHODS

This study adopted a perceptual load paradigm to examine the temporal processes of attentional modulation by incorporating conditions of perceptual load, distractor-target compatibility, and eccentricity.

RESULTS

The behavioral results showed that a high perceptual load significantly reduced attentional distraction caused by peripheral distractors. The event-related potential results further revealed that shorter P2 latencies were observed for peripheral distractors than for central distractors under a high perceptual load and that a suppressed compatibility effect with increasing load was reflected by the P3 component.

CONCLUSION

These findings suggested that (1) P2 and P3 components effectively captured different sides of attentional processing modulated by load (i.e., the filter processing of the object and the overall attentional resource allocation) and (2) response patterns of selective attention modulated by perceptual load were influenced by eccentricity. Our electrophysiological evidence confirmed the behavioral findings, indicating the neural mechanisms of attentional modulation.

Investigating the attentional focus to workplace-related soundscapes in a complex audio-visual-motor task using EEG

Introduction

In demanding work situations (e.g., during a surgery), the processing of complex soundscapes varies over time and can be a burden for medical personnel. Here we study, using mobile electroencephalography (EEG), how humans process workplace-related soundscapes while performing a complex audio-visual-motor task (3D Tetris). Specifically, we wanted to know how the attentional focus changes the processing of the soundscape as a whole.

Method

Participants played a game of 3D Tetris in which they had to use both hands to control falling blocks. At the same time, participants listened to a complex soundscape, similar to what is found in an operating room (i.e., the sound of machinery, people talking in the background, alarm sounds, and instructions). In this within-subject design, participants had to react to instructions (e.g., "place the next block in the upper left corner") and to sounds depending on the experimental condition, either to a specific alarm sound originating from a fixed location or to a beep sound that originated from varying locations. Attention to the alarm reflected a narrow attentional focus, as it was easy to detect and most of the soundscape could be ignored. Attention to the beep reflected a wide attentional focus, as it required the participants to monitor multiple different sound streams.

Results and discussion

Results show the robustness of the N1 and P3 event related potential response during this dynamic task with a complex auditory soundscape. Furthermore, we used temporal response functions to study auditory processing to the whole soundscape. This work is a step toward studying workplace-related sound processing in the operating room using mobile EEG.